There is known a technology that calculates a disparity data item of each point of a target object based on at least a pair of images of the target object captured around a vehicle using triangulation theory, and calculates, based on the disparity data items, distance information about the target object; the distance information includes a distance of each point of the target object relative to the vehicle. Then, the technology monitors the target object based on the distance information about the target object.
For example, Japanese Patent Application Publication No. H05-265547, which will be referred to as a published patent document, discloses a surround view monitoring apparatus based on the above technology. Specifically, the surround view monitoring apparatus obtains, based on a pair of images of a target object captured by a stereo camera installed in a vehicle, a distance distribution comprised of a distance of each point of the target object. Then, the surround view monitoring apparatus obtains three-dimensional distance information about the target object based on the distance distribution to thereby measure the shape and/or positional relationship between the target object and the vehicle.